For telescopic sights, in particular for precision long-barrel guns, it is well-known to illuminate the reticle of the telescopic sight by means of a special illumination assembly. In a conventional illuminated reticle, a potentiometer is arranged within a laterally protruding assembly (commonly referred to as “Turm” in the German art) of the sight, the potentiometer being actuated by the user via an externally accessible rotatable knob. The potentiometer is arranged within the circuit of a lamp being supplied from a battery. Instead of using a potentiometer, it is also known to use a rotary switch with a plurality of switching positions to which a resistance cascade is connected.
In this context one has a well-known problem, namely that the battery used for supplying current to the illuminated reticle is discharged too quickly when the illuminated reticle is switched on for a too long period of time or when it remains switched on inadvertently.
German Utility Model document DE 202 08 819 U1 describes a telescopic sight having a reticle illumination unit. The illumination unit comprises a rotary potentiometer, however, it further comprises a push switch, such that the illumination unit may be switched off or on in any rotary position of the potentiometer. By doing so, the rifleperson, for saving battery capacity, may switch the illumination unit off in the last set brightness position, and may switch it on again, if needed, in particular when a target object appears, wherein the same brightness as had been set before is immediately set.
This and other prior art illumination units for telescopic sights, operating with rotary potentiometers or the like, have the disadvantage that the brightness varies as a function of the particular characteristic of the potentiometer, when the rotary knob is rotated. The characteristic is conventionally linear. Therefore, the brightness gradually increases or decreases, respectively, when the rifleperson turns the rotary knob.
This approach does not take into account that the lamp used normally has a non-linear characteristic (radiation intensity vs. current consumption). The same applies for the sensitivity of the eye which, in addition, may substantially vary from rifleperson to rifleperson. All these characteristics are difficult to evaluate beforehand and may in no event be compensated by a standard potentiometer. In practice it is almost or entirely impossible to properly match the brightness adjustment to extreme light conditions.
The same considerations apply for the industrial mass production of such illumination units. The components supplied from the suppliers, namely in particular the lamps and the rotary potentiometers, also vary from one component to another and, in particular, from batch to batch.
One might theoretically consider to avoid the afore-discussed problems at least partially in that rotary switches in conjunction with resistance cascades are used, as already described, wherein the individual resistances within the resistance cascade are selected in accordance with the desired overall characteristic.
Such an approach, however, would require extreme efforts and would involve substantial production costs. Moreover, for technical and spatial reasons the number of resistances for such a resistance cascade would be limited, such that only an illumination adjustment with coarse resolution could be effected.
Moreover, for an exact representation of the characteristic the resistances would have to be individually selected and assembled for each unit.
Finally, prior art illumination units with rotary potentiometers have the disadvantage that the mechanical angle of rotation of the potentiometer is conventionally limited to a value of substantially less than 360°. Limit stops are provided at the two end positions of the rotary potentiometer which not only require certain efforts in production but may also be mechanically damaged under the rough conditions under which firearms are actually used.
It is, therefore, an object underlying the invention, to improve an illumination unit of the type specified at the outset such that these disadvantages are avoided.
In particular, an illumination unit shall be created which allows to be individually matched to existing characteristics by using relatively simple and low-cost means, even under mass production conditions. Furthermore, a limitation in the actuation of the adjustment element, such as limit stops or the like, shall be avoided, such that the brightness may be increased or decreased starting from any position of the adjustment element.